Scaling image with linear interpolation does not blend colours linearly
GIMP version: 2.10.22
Operating System: Linux (openSUSE Leap 15.2)
Package: flatpak from gimp.org installed yesterday
When scaling a tiny picture to extreme size, the blend between dark and bright pixels of the input image are clearly not linear and much brighter than expected. This effect should also increase the average brightness of pictures with lots of detail (changes between colours). Description of the bug
Reproduction
Is the bug reproducible? Always
Reproduction steps:
- Create 2x1 pixel image
- Fill left pixel with black and the right pixel with white
- Image -> Scale to 1024x512 with linear interpolation
- Colour pick from the middle (at x=512)
Expected result: mid-grey (128,128,128) at x=512
Actual result: light-grey (188,188,188) at x=512
Additional information
This worked as expected in version 2.8.22, except for that one must use a 2x2 picture to start with. (Version 2.8.22 appears to have a bug that 2x1 pictures are scaled with the "None" interpolation.)